Protein misfolding and abnormal aggregation is known to be characteristic of many diseases and often coincident with peptide mutations. Our long-term goal is to understand the effects of peptide mutations upon the relative energies of the various peptide secondary structures and how they are related to these diseases, with particular emphas placed on diseases related to collagen structure and Alzheimer's disease. With respect to the collagen related diseases, we suggest that these mutations cause errors in the H-bonding patterns of normal collagen. With respect to Alzheimer's disease, we suspect that mutations affect the relative amounts and positions of local alpha-helical structure in the protein, tau, which can change its propensity to be phosphoylated. Hyperphosphorylation has been directly related to the abnormal aggregation of tau which is a physiological symptom of Alzheimer's Disease. The specific aims of the proposed work will be the elucidation the structural factors that determine that determine the secondary structures of peptides using density functional and semi empirical molecular orbital theory, both in isolated (gas phase) and solvated completely geometrically optimized oligopeptides. This work will be coordinated with NMR structural determinations of the same peptides where possible. A second aim will be the application of these and other similar energetic studies to the improved understanding of the details of several diseases that involve mutated, misfolded and/or unnaturally aggregated peptides and proteins. The specific foci of these studies will be collagen-like triple helices (related to osteogenesis imperfecta, Ehlers-Danlos syndrome, Alport syndrome, Schmid metaphyseal chondrodysplasia and dystrophic epidermolysis bullosa) and the protein tau (involved in Alzheimer's disease). First principles (quantum mechanical) calculations will be used to determine the relative energies of the secondary structures of different peptides. The knowledge gleaned from these studies will be applied to determining the properties misfolded proteins that cause several diseases.